1. Field of the Invention
The present invention relates to a clutch mechanism of an outboard engine.
2. Description of the Related Art
In general, an outboard engine has a clutch mechanism which is remotely-operable to change over the direction of rotation of a propeller shaft between xe2x80x9cforwardxe2x80x9d and xe2x80x9creversexe2x80x9d passing through a xe2x80x9cneutralxe2x80x9d state. To enable such a change-over of direction of rotation, the propeller shaft has a push rod incorporated therein. The push rod is moved back and forth to bring a clutch dog into and out of engagement with the propeller shaft. This arrangement is generally known as xe2x80x9cshift-in and shift-outxe2x80x9d structure. A shift cam is typically used as means for effecting the back-and-forth movement of the push rod.
The shift cam has a cam profile which is defined by three curved recesses that are smoothly connected one to another. These three recesses have different depths corresponding to three shift positions, i.e., the xe2x80x9cforwardxe2x80x9d, xe2x80x9creversexe2x80x9d and xe2x80x9cneutralxe2x80x9d states, of the clutch mechanism. The above-mentioned push rod is normally spring-biased towards the cam, so as to rest in one of the three recesses, thus selecting one of the three shift positions.
There are two types of the shift cam: a vertically-movable shift cam which moves up and down to bring different recesses into engagement with the push rod; and a rotational shift cam which rotates within a horizontal plane. The rotational shift cam imparts to the operator a better feel of manipulation and is used mainly for large-sized outboard engines.
The shift cam is associated with a suitable means which retains the shift cam in the neutral position. For instance, a linearly-movable shift cam may have a detent mechanism with a rigid ball spring-biased into a dent formed in the back side, i.e., the side opposite to the recesses, of the shift cam.
Thus, the detent mechanism can easily be located in the vicinity of the shift cam, when the cam is of the linearly movable type. With the rotational shift cam, however, it is not easy to find a space in the close proximity of the shift cam for accommodating the detent mechanism. The detent mechanism therefore has to be disposed at a location spaced away from the shift cam, e.g., on a portion of a clutch rod.
The rotational shift cam has a stopper for preventing the cam from rotating beyond limit rotational positions. As in the case of the detent mechanism, the stopper cannot be disposed in the vicinity of the shift cam. The stopper is therefore arranged at a position remote from the shift cam, e.g., on a portion of the clutch rod.
During shifting from the forward position to the neutral position and from the neutral position to the reverse position, and vice versa, the end of the push rod engaging the shift cam has to slide along a peak or a crest between the two recesses of the cam profile, thus encountering a significant resistance or load, which impairs the feel of the shifting operation.
Locating the detent mechanism at a position remote from the shift cam allows the detent mechanism to act on the shift cam only indirectly. This leads to problems such as a time lag until the detent force is actually exerted on the shift cam. In addition, there is a risk that the clutch mechanism may be erroneously brought back into the shift-in condition even when the detent mechanism is operative.
It is also to be noted that assembly or setup of the clutch mechanism cannot be performed unless the shift cam is fixed exactly in the neutral position by the detent function. Fixing of the shift cam exactly at the neutral position is also essential for enabling confirmation of the shift-in and shift-out positions after the setup.
Likewise, locating the stopper at a place remote from the shift cam may lead to troubles such as unintentional continuation of the shift-in state despite safe functioning of the stopper.
In view of the foregoing, it is an object of the present invention to provide a clutch mechanism which is used in an outboard engine and which ensures full functioning of a detent mechanism and a stopper, while offering improved feel of the shifting operation.
To this end, according to the present invention, there is provided a clutch mechanism of an outboard engine, comprising: a remotely-operable shift cam for switching the direction of rotation of a propeller shaft in a gear case of the outboard engine; a clutch rod and a shift rod through which the shift cam is remotely operated; and an assist device provided to act between the clutch rod and the shift rod, the assist device including a drive member connected to the clutch rod, a driven member connected to the shift rod and driven by the drive member, and a resilient member disposed to act between the drive member and the driven member.
The drive member and the driven member may be rotary members, and the assist device may have a shift housing which rotatably supports and receives the rotary drive member and the rotary driven member. With this arrangement, the clutch mechanism may have a detent mechanism on the shift housing and which includes a rigid ball, a spring for urging the rigid ball against the outer peripheral surface of the rotary driven member, and a plurality of recesses formed in the outer peripheral surface of the rotary driven member, the spring urging and pressing the rigid ball into engagement with one of the recesses.
Preferably, the driven member is provided with a stopper projecting from the outer peripheral surface thereof, while the shift housing has a cylindrical hub surrounding and supporting the driven member, the cylindrical hub having a cutout portion which receives the stopper such that the range of rotational movement of the stopper is limited by both ends of the cutout portion, whereby the range of rotation of the driven member is limited.
Preferably, a projection for retaining the elastic member is provided on the drive member.
Preferably, the projection has an arcuate form concentric with the drive member.
The arrangement may be such that the end of the projection makes surface contact with a portion of the driven member.
Preferably, the spring which urges the rigid ball against the outer peripheral surface of the driven member is arranged to extend obliquely downward within the shift housing when viewed in side elevation.
The above and other objects, features and advantages of the present invention will become clear from the following description of a preferred embodiment with reference to the accompanying drawings.